The present invention relates to a track tensioning system for tracked vehicles, and more particularly, to a system that uses the endless track as a spring to resist suspension displacement caused by certain types of displacement forces.
Tracked vehicles, such as snowmobiles, have rear suspension systems generally including front and rear suspension arms pivotally mounted on a shaft rotatably connected to the frame of the tracked vehicle and a slide frame comprising a pair of laterally spaced suspension rails or longitudinal skids interconnected transversely on opposite sides of the machine. The suspension rails are in sliding contact with an endless belt that provides ice and snow surface contact and friction drive for the tracked vehicle. Where the movement of the suspension arms relative to the suspension rail is substantially limited to rotational motion, the suspension system referred to as fully coupled. As used herein, xe2x80x9cfully coupledxe2x80x9d means a suspension system where a displacement of any portion of the suspension rail causes immediate movement of the entire suspension rail, such as for example where the suspension forms parallelogram configuration.
In many current arrangements, a shackle or sliding block mechanism interconnects the rear suspension arm and the suspension rails to permit relative movement that includes a non-rotational component, such as a lateral or a longitudinal linear component (also referred to as lost motion). Such suspension systems are referred to as non-coupled. As used herein, xe2x80x9cnon-coupledxe2x80x9d refers to a suspension system in which displacement of the rear suspension arm relative to a suspension rail includes a linear component.
The non-coupled configuration allows the front and rear suspension arms to operate independent of one another, which was thought advantageous in the prior art because of favorable weight transfer characteristics that enhance traction. This independence, however, was found to result in rough and unsteady rides for the rider, particularly when the rear suspension of the track encounters an elevated mound of ice or snow or the upward side of a depression. This instability detracts from the enjoyment and the utility of the vehicle since there are many areas which, when traversed, will unduly subject the rider to severe jolts and stress.
The independent movement of the front and rear suspension arms adversely affects the tracked vehicle in several ways. First, track tension is not adequately maintained when there is extreme deflection of either one of the front or rear suspension arms. Extreme variations in track tension can reduce the comfort, control, track life and ultimately the safety of the rider.
Second, independent movement of the front and rear suspension arms in a non-coupled system requires the associated springs and shock absorbers to be sprung and dampened more stiffly because each must individually support the high loads when impact occurs at either the front or rear extreme of the suspension rails. That is, the springs and shock absorbers of each suspension arm must be stiff enough to withstand and control the full impact of the bump and weight of the tracked vehicle by itself. The required stiffness of the spring and shock absorber results in a less comfortable on normal terrain.
Third, when the front suspension arm of a non-coupled suspension deflects as it contacts a bump, the front suspension arm deflects more than the rear suspension arm. This results in an angle of incidence between the suspension rails and the bump. Unless the impact is then large enough to compress the rear suspension arm spring and shock absorber assembly, thereby flattening the angle of incidence, the suspension rails will act as a ramp forcing the rear of the tracked vehicle upward. At low to moderate speeds, the suspension rails angle in an upward incline due to the greater deflection of the front suspension arm than the rear suspension arm, causing the tracked vehicle to hop over the bump, imparting a secondary jolt that increases in intensity with the speed of the tracked vehicle.
These problems were successfully addressed in by the partially coupled suspension systems disclosed in U.S. Pat. No. 5,370,198 (Karpik); U.S. Pat. No. 5,667,031 (Karpik) and U.S. Pat. No. 5,881,834 (Karpik)(hereinafter xe2x80x9cthe Karpik Patentsxe2x80x9d). The Karpik Patents disclose a coupling system that permits some independent movement of the rear suspension arm relative to the front suspension arm. Once the rear suspension arm reaches the limit of its independent motion, the system becomes fully coupled.
The coupling system can also serve as a weight transfer mechanism that transmits an increasing percentage of the tracked vehicle""s weight to the front suspension arm and the forward end of the slide rail. Through the coupling system, the work of the spring and shock absorbers is shared by the front and rear suspension arms. By sharing forces acting on the suspension system generally between the front and rear suspensions arms, it is possible to use softer shock and spring calibrations than normally would be required to prevent the suspension system from bottoming out. The resulting softer shock and spring calibrations provide a more comfortable ride in normal terrain.
Assuming that the coupling system distributes forces acting on the suspension system between the front and rear suspension arms, the springs and shock absorber at the front suspension arm carries a portion of the force and the rear suspension arm carries the remainder of the force. The minimum theoretical shock and spring calibration must be set to handle the maximum anticipated force the suspension system will encounter. In order to maximize ride comfort on normal terrain, what is needed is a suspension system that reduces the shock and spring calibrations below this theoretical minimum, while still providing adequate resistance to extreme suspension displacement.
The present invention relates to a system for using the endless track on a tracked vehicle as a spring to supplement the biasing force of the suspension system during certain types of loads. The resulting increase in track tension resists further increases in perimeter length, hence resisting further suspension displacement. Consequently, the spring and shock absorber calibrations can be reduced to levels not previously possible.
The suspension system for suspending an endless track beneath a tracked vehicle chassis can be a fully coupled suspension, a partially coupled suspension or a non-coupled suspension. The suspension system includes at least one elongated suspension rail having a front portion, a rear portion and a bottom track-engaging portion. At least one suspension arm has an upper end adapted for pivotal connection to the vehicle chassis and a lower end pivotally connected to the suspension rail. The upper or lower ends of the suspension arm can optionally have a displacement with a non-linear component. A biasing mechanism provides a biasing force to bias the suspension rail away from the vehicle chassis. The track tensioning system coupled to the suspension arm applies a tensioning force to the endless track in response to linear and/or rotational displacement of the suspension arm. The tensioning force generates a supplemental force transmitted by the endless track that augments the biasing force of the biasing mechanism. In a suspension system with front and rear suspension arms, the track tensioning system can be coupled to the front or rear suspension arms.
A variety of other mechanism and/or conditions can be used to cause the track tensioning system to increase track tension. In one embodiment, the track tensioning system is coupled to a coupling system. The track tensioning system applies a tensioning force to the endless track when the coupling system is activated. In another embodiment, the track tensioning system applies a tensioning force to the endless track in response to a displacement of the rear portion of the suspension rail greater than a displacement of a front portion of the suspension rail. The track tensioning system can also be triggered when the suspension rail experiences a G-bump or a tail bump. In yet another embodiment, the track tensioning system increases perimeter length of the suspension system in response to displacement of the suspension arm. The increase in perimeter length generates a supplemental force transmitted by the endless track that augments the biasing force of the biasing mechanism.
The displacement of the suspension arm can include linear and/or rotational components that causes the tensioning system to increase track tension. The supplemental force generated by the tensioning system can be proportional or non-proportional to the magnitude of the displacement of the suspension arm.
Various track tensioning mechanisms can be used in connection with the present suspension system. In one embodiment, the track tensioning system comprises a tensioning wheel engaged with an inside surface of the endless track. A bracket pivotally coupled to the suspension system supports the tensioning wheel at a first end and is coupled to one of the suspension arms at a second end.
In another embodiment, the track tensioning system includes a rear wheel pivotally mounted to the rear portion of the suspension rail and a connector arm coupled to the rear suspension arm at a first end and to the rear wheel at a second end. The connector arm can be coupled to the axle of the rear wheel, the bracket supporting the rear wheel or a variety of other locations.
In yet another embodiment, the rear wheel at the rear of the suspension rail is on an axle. The axle slidingly engaged with a slot on the rear portion of the suspension rail. The connector arm couples the rear suspension arm the axle. The slot can be horizontal, a combination of horizontal and non-horizontal components, curvilinear, or a combination thereof. The shape of the slot can vary the incremental increase in track tension as a function of rear wheel displacement.
In another embodiment, the rear wheel slidingly engages with a sliding member on the rear portion of the suspension rail. A connector arm is coupled to the suspension arm at a first end and the sliding member at a second end. The sliding member can include a static track tensioning assembly. The connector arm can include an elastic portion.
In another embodiment, a pivot connects the front portion of the suspension rail to the rear portion. A connector arm is coupled to the suspension arm at a first end and the front portion of the suspension rail at a second end. In one embodiment, the connector arm is coupled to a front suspension arm.
The track tensioning system can be coupled to the suspension arm using an elastic member. The elastic member can be an elastomeric material, a spring, a shock absorber or a variety of other structures. In one embodiment, the supplemental force comprises a compressive force that resists an increase in perimeter length of the suspension system during suspension displacement. In another embodiment, the tensioning system decreases the tensioning force on the track in response to a decrease in perimeter length during suspension displacement.
The suspension system can optionally include a coupling system that couples the rear suspension arm to the suspension rail. The suspension system can be a fully coupled, a partially coupled or a non-coupled suspension system.